Techniques to mitigate bias drift for a memory device

ABSTRACT

Examples may include techniques to mitigate bias drift for memory cells of a memory device. A first memory cell coupled with a first word-line and a bit-line is selected for a write operation. A second memory cell coupled with a second word-line and the bit-line is de-selected for the write operation. First and second bias voltages are applied to the first word-line and the bit-line during the write operation to program the first memory cell. A third bias voltage is applied to the second word-line during the write operation to reduce or mitigate voltage bias to the second memory cell due to the second bias voltage applied to the bit-line to program the first memory cell.

CROSS REFERENCE TO RELATED APPLICATIONS

The present application is a continuation of U.S. application Ser. No.15/087,762 filed on Mar. 31, 2016. Application Ser. No. 15/087,762, ishereby incorporated herein by reference in its entirety.

TECHNICAL FIELD

Examples described herein are generally related to techniques tomitigate bias drift for memory cells included in a memory device.

BACKGROUND

Types of memory such as non-volatile memory may have reliability issuescaused by a tendency of a non-volatile memory cell to lose a memorystate over time. This loss of memory state over time may be referred toas drift. Drift may be an activated process that may be accelerated overtime by temperature or through electric field (e.g., sub-threshold biasvoltage across a memory cell).

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates an example system.

FIG. 2 illustrates an example first array portion.

FIG. 3 illustrates example first distributions.

FIG. 4 illustrates an example second array portion.

FIG. 5 illustrates an example graph.

FIG. 6 illustrates example second distributions.

FIG. 7 illustrates an example block diagram for an apparatus.

FIG. 8 illustrates an example of a logic flow.

FIG. 9 illustrates an example of a storage medium.

FIG. 10 illustrates an example computing platform.

DETAILED DESCRIPTION

As contemplated in the present disclosure, drift that may cause anon-volatile memory cell to lose its state may be an activated processaccelerated over time via repeated sub-threshold bias voltages acrossthe non-volatile memory cell (“bias-accelerated drift”). A type ofnon-volatile memory architecture that may include phase change memory(PCM) may be susceptible to bias-accelerated drift. In some examples,PCM may include memory cells composed of a chalcogenide phase changematerial (e.g., chalcogenide glass). Chalcogenide-based memory cells mayface possible reliability issues due to bias-accelerated drift. Forexample, a chalcogenide-based memory cell's threshold voltage maycontinue to increase with an increasing number of applied sub-thresholdvoltages on this type of memory cell. This may happen in a memoryarchitecture where de-selected memory cells receive sub-threshold biasvoltage pulses while a selected memory cell on a same bit-line (B-cell)or word-line (A-cell) is accessed. An increasing threshold voltage (Vt)may limit or reduce a read-window margin for memory cells. The limitedor reduced read-window margin may lead to higher bit error rates due tostored or set memory cell states having highly drifted Vts. An amount ofVt drift may depend on a total magnitude of a bias voltage pulse and anumber of pulses applied to a given memory cell.

A conventional way of handing drift or bias drift may be via use ofmemory controller initiated read-retries. An intention for read-retriesmay be capturing or thresholding memory cells having high Vts due tobias-accelerated drift. Another way of handling bias-accelerated driftmay be through periodic refreshes to existing addresses for memory cellsbefore these memory cells have Vts that drift beyond an available readwindow and causes bit errors. Both of these ways of handlingbias-accelerated drift may negatively impact system performance (e.g.,bandwidth/latency). These negative impacts to system performance may beunacceptable for high performance storage/memory systems. The examplesdescribed herein may address the above-mentioned and other challenges.

FIG. 1 illustrates an example system 100. In some examples, as shown inFIG. 1, system 100 includes memory cells 102, which may be configured inan array. Memory cells 102 may include, for example, a phase changematerial such as, but not limited to, a chalcogenide glass that may beswitched between crystalline and amorphous states with the applicationof heat produced by an electric current. A state (e.g.,crystalline/amorphous) of a phase change material may correspond with alogical value (e.g., 1 or 0) of one or more memory cells 102. Subjectmatter of this disclosure is not limited in this regard, and examplesmay include other types of architectures for memory devices.

According to some examples, system 100 may also include bit-lines 104and word-lines 106 coupled to memory cells 102, as shown in FIG. 1.Bit-lines 104 and word-lines 106 may be configured such that each memorycell included in memory cells 102 may be disposed at an intersection ofeach individual bit-line and word-line. Voltage biases may be applied toa target memory cell of memory cells 102 using a word-line fromword-lines 106 and a bit-line from among bit-lines 104 to program thetarget memory cell for a write operation. Respective bit-line drivers128 may be coupled to respective bit-lines 104 and respective word-linedrivers 126 may be coupled to respective word-lines 106 to facilitatedecoding/selection of memory cells 102, as shown in FIG. 1. Also,respective capacitors 130 may be coupled to respective bit-lines 104 andrespective word-lines 106, as shown in FIG. 1.

In some examples, system 100 may be a memory device that includes one ormore tiles 124. For these examples, the one or more tiles 124 may bearranged as a portion of a memory array that includes word-lines 106,bit-lines 104, and memory cells 102 that may be treated as a discreteunit during a selection operation of a target memory cell. That is, insome examples, each of the one or more tiles 124 is a unit of the memoryarray that is biased to select the target memory cell (e.g., a bit) inthe array. The one or more tiles 124 shown in FIG. 1 may include anarray of four word-lines and four bit-lines (4 WL×4 BL); however, othertile sizes may be used in other examples having either equal ratios ofword-lines and bit-lines or unequal ratios (e.g., 2 WL for every 1 BL).The one or more tiles 124 may be part of any memory layer of a stackedmemory configuration. For example, the one or more tiles 124 may be partof a memory layer formed on another memory layer. Additional word-linedrivers and/or bit-lines drivers may be provided for each memory layer.

According to some examples, bit-lines 104 may couple with a bit-lineelectrode or path 108, which may further couple with a bit-line supply132 that is configured to provide an electrical supply for bit-lines104. Also, word-lines 106 may couple to a word-line electrode or path110, which may further couple with a word-line supply 134 that isconfigured to provide an electrical supply for word-lines 106. Bit-lineelectrode 108 and the word-line electrode 110 may each be a current pathto memory cells 102. Word-line drivers 126 and bit-line drivers 128 mayeach include single or multiple transistors per electrode according tovarious examples. For examples where multiple transistors are used forword-line drivers 126 and bit-line drivers 128, the multiple transistorsmay be coupled to additional voltage supplies using additional word-lineand/or bit-line electrodes that may similarly comport with examplesdescribed herein. For example, a first word-line electrode may provide afirst voltage supply to one or more selected memory cells and secondword-line electrode may provide a second voltage supply to one or morede-selected memory cells.

In some examples, system 100 includes sensing circuitry 112 coupled toword-line electrode 110. For these examples, sensing circuitry 112 mayuse word-line electrode 110 as an electrical node for performing a readoperation, such as a sense operation, of one or more memory cellsincluded in memory cells 102. Sensing circuitry 112 may include avoltage comparator 114. For example, sensing circuitry 112 may include aword-line load connected to word-line electrode 110 to convert a currenton the word-line electrode 110 to a voltage that is a first input to thevoltage comparator 114. An equivalent word-line load may be connected toa reference current (not shown) to provide a voltage that is a secondinput to voltage comparator 114. When a particular word-line andbit-line are selected in system 100, the word-line load on word-lineelectrode 110 may convert the current on the selected word-line to avoltage. Leakage components of the current may be mitigated byrespectively selecting a bias voltage for all other unselectedword-lines and bit-lines for de-selected memory cells of memory cells102 that may reduce or minimize leakage. Capacitive components of thecurrent may be mitigated by allowing sufficient time for the capacitivecomponents to dissipate. The current that is converted to the firstinput to voltage comparator 114 may correspond with the current of theselected or target memory cell. The reference current may be selectedsuch that the current of the target or selected memory cell is lowerthan the reference current before snap-back of the target or selectedmemory cell and higher than the reference current after snap-back of thetarget memory cell. In this manner, an output of voltage comparator 114may be indicative of a state of the target or selected memory cell. Alatch (not shown) may be coupled to the voltage comparator 114 to storeinformation associated with the read operation.

According to some examples, system 100 may also include write circuitry116 coupled to word-line electrode 110. Write circuitry 116 may useword-line electrode 110 as an electrical node for performing a writeoperation, such as a SET or RESET operation, of one or more memory cellsfrom among memory cells 102. Write circuitry 116 may include a currentprofile generator 118 that generates a current profile for performingthe write operation.

In some examples, memory device 100 may also include components of aselection module 120 coupled to word-line electrode 110.Current-limiting circuitry 122 of selection module 120 may be coupled toword-line electrode 110 to facilitate a selection operation of one ormore memory cells of memory cells 102 using word-line electrode 110. Theselection operation may precede a read/write operation and place thetarget or selected memory cell in a state to receive a read/writeoperation. During selection, a targeted memory cell may be moved from asub-threshold region of operation to a region of operation above athreshold region of operation by applying a voltage bias across thetarget or selected memory cell. The voltage bias to achieve selection ofthe targeted memory cell is provided by word-line and bit-line drivercircuitry (e.g., of the selection module 120) of the respectiveword-line and bit-line for the targeted memory cell in conjunction withcurrent-limiting circuitry 122. Word-line and bit-line bias for therespective word-line and bit-line may be chosen such that, incombination, an overall voltage bias is applied across the target orselected memory cell that is sufficient to bring the targeted orselected memory cell above a threshold voltage (Vt). In the presentexample, “above Vt” may refer to a region of operation of a target orselected memory cell that is capable of conducting sufficient currentfor a write operation, although a smaller current may maintain thetarget or selected memory cell in the region of operation. Thetransition from sub-threshold to Vt or above a Vt region may involve a‘snap-back’ event where the voltage sustained by the target cell for agiven current through the cell is suddenly reduced. Current limitingcircuitry 122 may limit the current of word-line electrode 110 toprevent damaging the target or selected memory cell with excessivecurrent. That is, limiting the maximum current of word-line electrode110 may also limit the maximum current through the memory cells 102. Thelimiting function may be ineffective during a time that word-lineelectrode 110 and a word-line decoding path of the target word-line arecharging to a steady state.

According to some examples, current-limiting circuitry 122 may be placedon whichever of word-line electrode 110 or bit-line electrode 108 thathas a lower capacitance in order to reduce or minimize a transientcurrent after snap-back of one or more memory cells 102 to a level thatreduces damage or disturbance of memory cells 102. In the example shownin FIG. 1, current-limiting circuitry 122 is placed on word-lineelectrode 110.

In some examples, current-limiting circuitry 122 may include a currentmirror circuit. Current-limiting circuitry 122 may include a transistorgate that is configured to limit a current of word-line electrode 110 toa maximum current level. For example, the transistor may be an n-typetransistor having a gate that is controlled to an analog level such thatthe transistor delivers up to a maximum desired current.Current-limiting circuitry 122 may be enabled by applying a gate voltageto the transistor. Selection module 120 may include additional controlcircuitry to facilitate decoding of a target memory cell of the one ormore memory cells 102 such that the target or selected memory cell ismoved from a subthreshold region of operation to a region of operationabove Vt, where Vt is a function of current.

Although example types of memory included in system 100 have beendescribed as including non-volatile types of memory such as PCM, thisdisclosure is not limited to PCM. In some examples other types ofnon-volatile memory including, but not limited to, types of volatilememory such as those associated with NAND or NOR technologies arecontemplated by this disclosure. Also, other non-volatile types ofmemory included in a 3-D cross-point memory architecture that may bebyte addressable are contemplated by this disclosure. These blockaddressable or byte addressable non-volatile types of memory mayinclude, but are not limited to, multi-threshold level NAND flashmemory, NOR flash memory, single or multi-level phase change memory(PCM), resistive memory, nanowire memory, ferroelectric transistorrandom access memory (FeTRAM), magnetoresistive random access memory(MRAM) memory that incorporates memristor technology, or spin transfertorque MRAM (STT-MRAM), or a combination of any of the above, or othernon-volatile memory types.

FIG. 2 illustrates an example array portion 200. In some examples, arrayportion 200 as shown in FIG. 2, includes memory cells 202-1 to 202-4,bit-lines (BLs) 204-1, 204-2 and word-lines (WLs) 206-1, 206-2. Arrayportion 200 may have memory cells 202-1 to 202-4 arranged to be atintersections between WLs and BLs that may be metal lines used foraccess (write or read operations) to these memory cells. Similar to asdescribed above for system 100, a targeted memory cell of memory cells202-1 to 202-4 may be selected by applying a relevant voltage biasacross one of WLs 206-1 or 206-2 and one of BLs 204-1 or 204-2 such thata total differential voltage across the selected memory cell exceeds aVt for the selected memory cell during an access. For example, during awrite operation, bias voltages on a given WL of WLs 206-1 or 206-2(e.g., provided by a WL electrode) or a given BL of BLs 204-1 or 204-2(e.g., provided by a BL electrode) may be adjusted to allow forsufficient current to flow through the selected memory cell to programthe selected memory cell into a correct state (e.g., SET or RESET).

According to some examples, shaded memory cell 202-1 may be a selectedmemory cell. As the selected memory cell, memory cell 202-1 may receivea total bias voltage to deliver sufficient current and voltage forprogramming memory cell 202-1 during a write operation. As shown in FIG.2, the total bias voltage (e.g., 7V) may be delivered over WL 206-1 fromWL electrode 210 that provides WL voltage bias 211 and over BL 204-1from BL electrode 220 that provides BL voltage bias 221 to generate cellvoltage bias 212 at memory cell 202-1 from a combination of WL voltagebias 211 and BL voltage bias 221. In some examples, WL voltage bias 211,as shown in FIG. 2, may be a negative voltage bias and BL voltage bias221 may have a positive voltage bias. Unshaded memory cells 202-2, 202-3and 202-4 may be de-selected memory cells. De-selected memory cell 202-2on the same WL as selected memory cell 202-1 may be referred to as anA-cell. De-selected memory cell 202-3 on the same BL as selected memorycell 202-1 may be referred to as a B-cell. Cell voltage signal 213 mayrepresent a first portion of the total bias voltage delivered toselected memory cell 202-1 that is also delivered to memory cell 202-2over WL 206-1 from WL electrode 210 to provide WL voltage bias 211. Cellvoltage bias 214 may represent a second portion of the total biasvoltage delivered to selected memory cell 202-1 that is also deliveredto memory cell 202-3 over BL 204-1 from BL electrode 220 to provide BLvoltage bias 221.

In some examples, WL voltage bias 211 and BL voltage bias 221, whentaken separately, are both at sub-threshold voltage biases (e.g., belowVt). These sub-threshold voltage biases may vary in magnitude andduration depending on an operation being performed on a selected memorycell. Typically, a highest amount of voltage bias may be required for atype of write operation such as a RESET operation where a large amountof current may be required though a selected memory cell for programmingthe selected memory cell. At least a portion of this higher amount ofvoltage bias for a RESET operation may be delivered to de-selectedmemory cells in a similar manner as mentioned above for de-selectedmemory cells 202-2 and 202-3. This higher amount of voltage bias for theRESET operation may cause bias-accelerated drift.

FIG. 3 illustrates example distributions 300. In some examples, as shownin FIG. 3, distributions 300 includes a first threshold distribution 310(pre-drift) and a second threshold distribution 320 (post-drift). Forthese examples, threshold distributions 310 and 320 may reflectbias-accelerated drift for de-selected memory cells caused primarilywhen these de-selected memory cells receive at least a portion ofvoltage bias for a write operation such as a RESET operation. Forexample, as mentioned above for de-selected memory cells 202-2 or 202-3shown in FIG. 2.

In some examples, accumulation of multiple sub-threshold bias voltageson de-selected memory cells may cause a loss of an available read windowor margin. For example, as shown in FIG. 3, read margin 325 between SETVt and read demarcation voltage (VDM) for threshold distribution 320(post-drift) is substantially smaller or narrower than read margin 315for threshold distribution 310 (pre-drift). The smaller or narrower readmargin 325 may ultimately result in higher bit error rates for aprogrammed read VDM

FIG. 4 illustrates an example array portion 400. In some examples, arrayportion 400 as shown in FIG. 4, includes memory cells 402-1 to 402-4,BLs 404-1, 404-2 and WLs 406-1, 406-2. Similar to array portion 200shown in FIG. 2, array portion 400 may be part of a 3-D cross-pointmemory array and may operate in a similar manner as described above forarray portion 200. However, different than what was described above forarray portion 200, a biasing scheme may be implemented that mitigates orreduces bias-accelerated drift.

According to some examples, to mitigate bias-accelerated drift, anadditional positive voltage may be applied on a WL of deselected memorycells (e.g., provided by a second WL electrode). For example, as shownin FIG. 4, memory cell 402-1 is the selected memory cell and receives atotal bias voltage (e.g., 7 volts (V)) from WL voltage bias 411 providedby WL electrode 410 and BL voltage bias 421 provided BL electrode 420 togenerate cell voltage bias 412. However, the additional positive voltagefrom a second WL electrode 430 to provide C-cell voltage bias 431 may beapplied on WL 406-2 to reduce differential voltage bias on memory cell402-3 caused by BL voltage bias 421 provided by BL electrode 420. Thesolid line portion of cell voltage bias 414 may represent the additionalpositive voltage that reduces differential voltage bias on memory cell402-3 caused by BL voltage bias 421 that is shown as the dotted-lineportion of cell voltage bias 414. As shown in FIG. 4, C-cell voltagebias 431 may be less than BL voltage bias 421 (e.g., 1V vs. 3.5V).C-cell voltage bias 431 may also be turned on or provided to de-selectedmemory cells 402-3 and 402-4 during a selection operation of a writealgorithm to mitigate possible false selection of these memory cellswhen selecting memory cell 402-1.

In some examples, C-cell voltage bias 431 may be enabled or applied tode-selected memory cell 402-3 during a write operation such as a RESEToperation. The RESET operation may have a voltage bias on a memory cellthat may be substantially higher than another type of write operationsuch as a SET operation to achieve a required current delivery. Also,the scheme shown in FIG. 4 may mainly reduce bias-accelerated driftimpacts on B-cells (e.g., memory cell 402-3) since a higher voltage biasmay be applied on BLs during write operations. As described in moredetail below, a reduction of 1V of voltage bias across a given memorycell may noticeably mitigate bias-accelerated drift when the number ofbias cycles surpasses 1,000 and substantially mitigate bias-accelerateddrift when the number of bias cycles surpasses 1,000,000.

According to some examples, C-cell voltage bias 431 applied to WL 406-2from WL electrode 430 does not impact differential biases on both memorycells 402-1 and 402-2 as these memory cells are on WL 406-1. Forexample, as shown in FIG. 4, cell voltage biases 412 and 413 do notinclude the positive bias voltage from C-cell voltage bias 431. Also,since memory cell 402-4 is not subject to voltage bias from BL voltagebias 421, C-cell voltage bias 431 indicates only the relatively smallervoltage bias applied to memory cell 402-4.

FIG. 5 illustrates an example graph 500. In some examples, as shown inFIG. 5, graph 500 depicts a comparison of read margin loss in millivolts(mV) for a scheme that includes application of a C-cell voltage bias asmentioned above for FIG. 4 and for a scheme that does not include anapplication of a C-cell voltage bias. For these examples, an appliedC-cell voltage bias may be 1V. The scheme, for example, may be appliedto 3-D cross-point memory architecture including PCM such aschalcogenide glass.

In some examples, as shown in FIG. 5, a noticeable reduction in readmargin loss starts to occur when a number of bias cycles exceeds 1,000.Also, at 1,000,000 bias cycles read margin loss reduction is shown ingraph 500 to be approximately 150 mV.

FIG. 6 illustrates example distributions 600. In some examples,distributions include a first threshold distribution 610 (0 biascycles), a second threshold distribution 620 (1e+6 bias cycles/withoutC-cell bias voltage) and a third threshold distribution 630 (1e+6 biascycles/with C-cell bias voltage. For these examples, thresholddistributions 610, 620 and 630 may reflect bias-accelerated drift forde-selected memory cells caused primarily when these de-selected memorycells receive at least a portion of voltage bias from a BL voltage biasfor a programming or write operation such as a RESET operation. Forexample, as mentioned above for de-selected memory cell 402-3 shown inFIG. 4.

In some examples, threshold voltage distribution 610 indicates that readmargin 615 may have a read margin or window between SET Vt and read VDMof 300 mV when 0 bias cycles have occurred. Threshold voltagedistribution 620 indicates that read margin 615 may have been reduced to75 mV after 1e+6 (1,000,000) bias cycles when no C-cell bias voltage hasbeen applied to de-selected memory cells. Comparatively, thresholdvoltage distribution 630 shows that read margin 615 has only beenreduced to 225 mV after 1e+6 bias cycles. For these examples, a 2× lessreduction (75 mV vs. 150 mV) in read margin reduction may be achievedwhen applying a C-cell bias voltage during a RESET operation. A smallerread margin reduction may lead to fewer bit errors and a need for fewerread retries. Some voltage overhead may be needed to deliver or applyC-cell voltage bias to de-selected memory cells during RESET operations.However, fewer bit errors and fewer read retries may be more beneficialto system performance when compared to costs associated with additionalvoltage overhead.

According to some examples, a scheme may be implemented to selectivelyreduce actual bit-line voltage bias applied to memory cells included ina non-volatile memory device (e.g., arranged as a 3-D cross-point memoryarray). For these examples, at least some memory cells may be programmedusing a lower bias voltage for RESET operations (e.g., memory cellsphysically located closer to bit-line drivers). For these lower biasvoltage memory cells, a C-cell bias voltage may not be applied tode-selected memory cells on the same BL. Also, other memory cellsneeding a higher bias voltage for RESET operations (e.g., memory cellsphysically located farthest or farther from bit-line drivers) may have aC-cell bias voltage applied to de-selected memory cells on the same BL.This scheme may strike a balance between both reducing voltage overheadand improving performance by reducing bias-accelerated drift forde-selected memory cells subject to higher levels of bias voltage duringwrite operations such a RESET operation.

FIG. 7 illustrates an example block diagram for an apparatus 700.Although apparatus 700 shown in FIG. 7 has a limited number of elementsin a certain topology, it may be appreciated that the apparatus 700 mayinclude more or less elements in alternate topologies as desired for agiven implementation.

The apparatus 700 may be supported by circuitry 720 and apparatus 700may be a controller maintained at a memory device or with a memorysystem. The memory device may be coupled with or included in a hostcomputing platform. Circuitry 720 may be arranged to execute one or moresoftware or firmware implemented logic, components or modules 722-a(e.g., implemented, at least in part, by a storage controller of astorage device). It is worthy to note that “a” and “b” and “c” andsimilar designators as used herein are intended to be variablesrepresenting any positive integer. Thus, for example, if animplementation sets a value for a=3, then a complete set of software orfirmware for logic, components or modules 722-a may include logic 722-1,722-2 or 722-3. Also, at least a portion of “logic” may besoftware/firmware stored in computer-readable media, and although thelogic is shown in FIG. 7 as discrete boxes, this does not limit logic tostorage in distinct computer-readable media components (e.g., a separatememory, etc.).

According to some examples, circuitry 720 may include a processor orprocessor circuitry. The processor or processor circuitry can be any ofvarious commercially available processors, including without limitationan AMD® Athlon®, Duron® and Opteron® processors; ARM® application,embedded and secure processors; IBM® and Motorola® DragonBall® andPowerPC® processors; IBM and Sony® Cell processors; Intel® Atom®,Celeron®, Core (2) Duo®, Core i3, Core i5, Core i7, Itanium®, Pentium®,Xeon®, Xeon Phi® and XScale® processors; and similar processors.According to some examples circuitry 720 may also include one or moreapplication-specific integrated circuits (ASICs) and at least some logic722-a may be implemented as hardware elements of these ASICs.

According to some examples, apparatus 700 may include a selection logic722-1. Selection logic 722-1 may be a logic and/or feature executed bycircuitry 720 to select a first memory cell coupled with a firstword-line and a bit-line for a write operation and de-select a secondmemory cell coupled with a second word-line and the bit-line, the secondmemory cell de-selected for the write operation. For these examples, theselection of the first memory cell and the de-selection of the secondmemory cell may be responsive to access request 710 and may be initiatedvia selection/de-selection 715.

In some examples, apparatus 700 may also include a program logic 722-2.Program logic 722-2 may be a logic and/or feature executed by circuitry720 to cause a first bias voltage to be applied to the first word-lineand a second bias voltage to be applied to the bit-line during the writeoperation to program the first memory cell. For these examples, program730 may include a RESET operation to program the first memory cell.

According to some examples, apparatus 700 may also include a mitigationlogic 722-3. Mitigation logic may be a logic and/or feature executed bycircuitry 720 to cause a third bias voltage to be applied to the secondword-line during the write operation to provide the third bias voltageto the second memory cell to reduce voltage bias to the second memorycell due to the second bias voltage applied to the bit-line to programthe first memory cell, the third bias voltage less that the second biasvoltage. For these examples, voltage bias mitigation 735 may cause thethird bias voltage to be applied to the second word-line such thatvoltage bias to the second memory cell may be reduced by at least 1Vduring the write operation. Examples are not limited to a reduction ofat least 1V, other reductions of greater of lesser volts arecontemplated.

Included herein is a set of logic flows representative of examplemethodologies for performing novel aspects of the disclosedarchitecture. While, for purposes of simplicity of explanation, the oneor more methodologies shown herein are shown and described as a seriesof acts, those skilled in the art will understand and appreciate thatthe methodologies are not limited by the order of acts. Some acts may,in accordance therewith, occur in a different order and/or concurrentlywith other acts from that shown and described herein. For example, thoseskilled in the art will understand and appreciate that a methodologycould alternatively be represented as a series of interrelated states orevents, such as in a state diagram. Moreover, not all acts illustratedin a methodology may be required for a novel implementation.

A logic flow may be implemented in software, firmware, and/or hardware.In software and firmware embodiments, a logic flow may be implemented bycomputer executable instructions stored on at least one non-transitorycomputer readable medium or machine readable medium, such as an optical,magnetic or semiconductor storage. The embodiments are not limited inthis context.

FIG. 8 illustrates an example of a logic flow 800. Logic flow 800 may berepresentative of some or all of the operations executed by one or morelogic, features, or devices described herein, such as apparatus 700.More particularly, logic flow 800 may be implemented by one or more ofselection logic 722-1, program logic 722-2 or mitigation logic 722-3.

According to some examples, logic flow 800 at block 802 may select afirst memory cell coupled with a first word-line and a bit-line for awrite operation. For these examples, selection logic 722-1 may selectthe first memory cell.

In some examples, logic flow 800 at block 804 may de-select a secondmemory cell coupled with a second word-line and the bit-line for thewrite operation. For these examples, selection logic 722-1 may de-selectthe second memory cell.

According to some examples, logic flow 800 at block 806 may apply afirst bias voltage to the first word-line and a second bias voltage tothe bit-line during the write operation to program the first memorycell. For these examples, program logic 722-2 may cause the first andsecond bias voltages to be applied to the first word-line and thebit-line to program the first memory cell.

In some examples, logic flow 800 at block 808 may apply a third biasvoltage to the second word-line during the write operation to reducevoltage bias to the second memory cell due to the second bias voltageapplied to the bit-line to program the first memory cell, the third biasvoltage less than the second bias voltage. For these examples,mitigation logic 722-3 may cause the third bias voltage to be applied tothe second word-line.

FIG. 9 illustrates an example of a first storage medium. As shown inFIG. 9, the first storage medium includes a storage medium 900. Thestorage medium 900 may comprise an article of manufacture. In someexamples, storage medium 900 may include any non-transitory computerreadable medium or machine readable medium, such as an optical, magneticor semiconductor storage. Storage medium 900 may store various types ofcomputer executable instructions, such as instructions to implementlogic flow 800. Examples of a computer readable or machine readablestorage medium may include any tangible media capable of storingelectronic data, including volatile memory or non-volatile memory,removable or non-removable memory, erasable or non-erasable memory,writeable or re-writeable memory, and so forth. Examples of computerexecutable instructions may include any suitable type of code, such assource code, compiled code, interpreted code, executable code, staticcode, dynamic code, object-oriented code, visual code, and the like. Theexamples are not limited in this context.

FIG. 10 illustrates an example computing platform 1000. In someexamples, as shown in FIG. 10, computing platform 1000 may include amemory system 1030, a processing component 1040, other platformcomponents 1050 or a communications interface 1060. According to someexamples, computing platform 1000 may be implemented in a computingdevice.

According to some examples, memory system 1030 may include a controller1032 and memory devices(s) 1034. For these examples, logic and/orfeatures resident at or located at controller 1032 may execute at leastsome processing operations or logic for apparatus 700 and may includestorage media that includes storage medium 900. Also, memory device(s)1034 may include similar types of non-volatile memory (not shown) thatare described above for system 100, array portion 200 or array portion400 shown in FIGS. 1, 2 and 4. In some examples, controller 1032 may bepart of a same die with memory device(s) 1034. In other examples,controller 1032 and memory device(s) 1034 may be located on a same dieor integrated circuit with a processor (e.g., included in processingcomponent 1040). In yet other examples, controller 1032 may be in aseparate die or integrated circuit coupled with memory device(s) 1034.

According to some examples, processing component 1040 may includevarious hardware elements, software elements, or a combination of both.Examples of hardware elements may include devices, logic devices,components, processors, microprocessors, circuits, processor circuits,circuit elements (e.g., transistors, resistors, capacitors, inductors,and so forth), integrated circuits, ASIC, programmable logic devices(PLD), digital signal processors (DSP), FPGA/programmable logic, memoryunits, logic gates, registers, semiconductor device, chips, microchips,chip sets, and so forth. Examples of software elements may includesoftware components, programs, applications, computer programs,application programs, system programs, software development programs,machine programs, operating system software, middleware, firmware,software modules, routines, subroutines, functions, methods, procedures,software interfaces, APIs, instruction sets, computing code, computercode, code segments, computer code segments, words, values, symbols, orany combination thereof. Determining whether an example is implementedusing hardware elements and/or software elements may vary in accordancewith any number of factors, such as desired computational rate, powerlevels, heat tolerances, processing cycle budget, input data rates,output data rates, memory resources, data bus speeds and other design orperformance constraints, as desired for a given example.

In some examples, other platform components 1050 may include commoncomputing elements, such as one or more processors, multi-coreprocessors, co-processors, memory units, chipsets, controllers,peripherals, interfaces, oscillators, timing devices, video cards, audiocards, multimedia I/O components (e.g., digital displays), powersupplies, and so forth. Examples of memory units associated with eitherother platform components 1050 or storage system 1030 may includewithout limitation, various types of computer readable and machinereadable storage media in the form of one or more higher speed memoryunits, such as read-only memory (ROM), RAM, DRAM, DDR DRAM, synchronousDRAM (SDRAM), DDR SDRAM, SRAM, programmable ROM (PROM), EPROM, EEPROM,flash memory, ferroelectric memory, SONOS memory, polymer memory such asferroelectric polymer memory, nanowire, FeTRAM or FeRAM, ovonic memory,phase change memory, memristers, STT-MRAM, magnetic or optical cards,and any other type of storage media suitable for storing information.

In some examples, communications interface 1060 may include logic and/orfeatures to support a communication interface. For these examples,communications interface 1060 may include one or more communicationinterfaces that operate according to various communication protocols orstandards to communicate over direct or network communication links.Direct communications may occur through a direct interface via use ofcommunication protocols or standards described in one or more industrystandards (including progenies and variants) such as those associatedwith the SMBus specification, the PCIe specification, the NVMespecification, the SATA specification, SAS specification or the USBspecification. Network communications may occur through a networkinterface via use of communication protocols or standards such as thosedescribed in one or more Ethernet standards promulgated by the IEEE. Forexample, one such Ethernet standard may include IEEE 802.3-2012, Carriersense Multiple access with Collision Detection (CSMA/CD) Access Methodand Physical Layer Specifications, Published in December 2012(hereinafter “IEEE 802.3”).

Computing platform 1000 may be part of a computing device that may be,for example, user equipment, a computer, a personal computer (PC), adesktop computer, a laptop computer, a notebook computer, a netbookcomputer, a tablet, a smart phone, embedded electronics, a gamingconsole, a server, a server array or server farm, a web server, anetwork server, an Internet server, a work station, a mini-computer, amain frame computer, a supercomputer, a network appliance, a webappliance, a distributed computing system, multiprocessor systems,processor-based systems, or combination thereof. Accordingly, functionsand/or specific configurations of computing platform 1000 describedherein, may be included or omitted in various embodiments of computingplatform 1000, as suitably desired.

The components and features of computing platform 1000 may beimplemented using any combination of discrete circuitry, ASICs, logicgates and/or single chip architectures. Further, the features ofcomputing platform 1000 may be implemented using microcontrollers,programmable logic arrays and/or microprocessors or any combination ofthe foregoing where suitably appropriate. It is noted that hardware,firmware and/or software elements may be collectively or individuallyreferred to herein as “logic”, “circuit” or “circuitry.”

Although not depicted, any system can include and use a power supplysuch as but not limited to a battery, AC-DC converter at least toreceive alternating current and supply direct current, renewable energysource (e.g., solar power or motion based power), or the like.

One or more aspects of at least one example may be implemented byrepresentative instructions stored on at least one machine-readablemedium which represents various logic within the processor, which whenread by a machine, computing device or system causes the machine,computing device or system to fabricate logic to perform the techniquesdescribed herein. Such representations may be stored on a tangible,machine readable medium and supplied to various customers ormanufacturing facilities to load into the fabrication machines thatactually make the logic or processor.

Various examples may be implemented using hardware elements, softwareelements, or a combination of both. In some examples, hardware elementsmay include devices, components, processors, microprocessors, circuits,circuit elements (e.g., transistors, resistors, capacitors, inductors,and so forth), integrated circuits, ASICs, PLDs, DSPs, FPGAs, memoryunits, logic gates, registers, semiconductor device, chips, microchips,chip sets, and so forth. In some examples, software elements may includesoftware components, programs, applications, computer programs,application programs, system programs, machine programs, operatingsystem software, middleware, firmware, software modules, routines,subroutines, functions, methods, procedures, software interfaces, APIs,instruction sets, computing code, computer code, code segments, computercode segments, words, values, symbols, or any combination thereof.Determining whether an example is implemented using hardware elementsand/or software elements may vary in accordance with any number offactors, such as desired computational rate, power levels, heattolerances, processing cycle budget, input data rates, output datarates, memory resources, data bus speeds and other design or performanceconstraints, as desired for a given implementation.

Some examples may include an article of manufacture or at least onecomputer-readable medium. A computer-readable medium may include anon-transitory storage medium to store logic. In some examples, thenon-transitory storage medium may include one or more types ofcomputer-readable storage media capable of storing electronic data,including volatile memory or non-volatile memory, removable ornon-removable memory, erasable or non-erasable memory, writeable orre-writeable memory, and so forth. In some examples, the logic mayinclude various software elements, such as software components,programs, applications, computer programs, application programs, systemprograms, machine programs, operating system software, middleware,firmware, software modules, routines, subroutines, functions, methods,procedures, software interfaces, API, instruction sets, computing code,computer code, code segments, computer code segments, words, values,symbols, or any combination thereof.

According to some examples, a computer-readable medium may include anon-transitory storage medium to store or maintain instructions thatwhen executed by a machine, computing device or system, cause themachine, computing device or system to perform methods and/or operationsin accordance with the described examples. The instructions may includeany suitable type of code, such as source code, compiled code,interpreted code, executable code, static code, dynamic code, and thelike. The instructions may be implemented according to a predefinedcomputer language, manner or syntax, for instructing a machine,computing device or system to perform a certain function. Theinstructions may be implemented using any suitable high-level,low-level, object-oriented, visual, compiled and/or interpretedprogramming language.

Some examples may be described using the expression “in one example” or“an example” along with their derivatives. These terms mean that aparticular feature, structure, or characteristic described in connectionwith the example is included in at least one example. The appearances ofthe phrase “in one example” in various places in the specification arenot necessarily all referring to the same example.

Some examples may be described using the expression “coupled” and“connected” along with their derivatives. These terms are notnecessarily intended as synonyms for each other. For example,descriptions using the terms “connected” and/or “coupled” may indicatethat two or more elements are in direct physical or electrical contactwith each other. The term “coupled,” however, may also mean that two ormore elements are not in direct contact with each other, but yet stillco-operate or interact with each other.

The follow examples pertain to additional examples of technologiesdisclosed herein.

Example 1

An example memory device may include a first memory cell coupled with afirst word-line and a bit-line. The first memory cell may be selectedfor a write operation. The memory device may also include a secondmemory cell coupled with a second word-line and the bit-line. The secondmemory cell may be de-selected for the write operation. The memorydevice may also include a first word-line electrode coupled with thefirst word-line to provide a first bias voltage to the first memory cellduring the write operation. The memory device may also include abit-line electrode coupled with the bit-line to provide a second biasvoltage to the first memory cell during the write operation. The firstand second bias voltages may cause the first memory cell to beprogrammed. The memory device may also include a second word-lineelectrode coupled with the second word-line to provide a third biasvoltage to the second memory cell during the write operation to reducevoltage bias to the second memory cell due to the second bias voltageapplied to the bit-line. The third bias voltage may be less than thesecond bias voltage.

Example 2

The memory device of example 1, the first and third bias voltages may beseparate positive voltage biases.

Example 3

The memory device of example 1, the third bias voltage may reducevoltage bias to the second memory cell by at least 1 volt during thewrite operation.

Example 4

The memory device of example 1, the write operation may be a RESEToperation to program the first memory cell.

Example 5

The memory device of example 1 may also include one or more additionalmemory cells coupled with the bit-line. The memory device may alsoinclude a bit-line driver coupled with the bit-line. For these examples,the first memory cell may be physically located on the bit-line in aposition farthest away from the bit-line driver as compared to thesecond memory cell and the one or more additional memory cells.

Example 6

The memory device of example 1, the first and second memory cells mayinclude non-volatile memory.

Example 7

The memory device of example 6, the non-volatile memory may includephase change memory that uses chalcogenide phase change material, flashmemory, ferroelectric memory, SONOS memory, polymer memory, FeTRAM,FeRAM, ovonic memory, nanowire, EEPROM, PCM, memristors or STT-MRAM.

Example 8

An example method may include selecting a first memory cell coupled witha first word-line and a bit-line for a write operation. The method mayalso include de-selecting a second memory cell coupled with a secondword-line and the bit-line for the write operation. The method may alsoinclude applying a first bias voltage to the first word-line and asecond bias voltage to the bit-line during the write operation toprogram the first memory cell. The method may also include applying athird bias voltage to the second word-line during the write operation toreduce voltage bias to the second memory cell due to the second biasvoltage applied to the bit-line to program the first memory cell. Forthese examples, the third bias voltage may be less than the second biasvoltage.

Example 10

The method of example 8, the first and third bias voltages may beseparate positive voltage biases.

Example 11

The method of example 8, the third bias voltage may reduce voltage biasto the second memory cell by at least 1 volt during the write operation.

Example 12

The method of example 8, the write operation may be a RESET operation toprogram the first memory cell.

Example 13

The method of example 8, the first memory cell may be physically locatedon the bit-line in a position farthest away from a bit-line driver forthe bit-line as compared to the second memory cell and one or moreadditional memory cells also coupled with the bit-line.

Example 13

The method of example 8, the first and second memory cells may includenon-volatile memory.

Example 14

The method of example 13, the non-volatile memory may include phasechange memory that uses chalcogenide phase change material, flashmemory, ferroelectric memory, SONOS memory, polymer memory, FeTRAM,FeRAM, ovonic memory, nanowire, EEPROM, PCM, memristors or STT-MRAM.

Example 15

An example at least one machine readable medium may include a pluralityof instructions that in response to being executed by a system may causethe system to carry out a method according to any one of examples 8 to14.

Example 16

An example apparatus may include means for performing the methods of anyone of examples 8 to 14.

Example 17

An example system may include a first memory cell coupled with a firstword-line and a bit-line. The first memory cell may be selected for awrite operation. The system may also include a second memory cellcoupled with a second word-line and the bit-line. The second memory cellmay be de-selected for the write operation. The system may also includea controller that includes logic, at least a portion of which isimplemented as hardware. For these examples, the logic may cause a firstbias voltage to be applied to the first word-line and a second biasvoltage to be applied to the bit-line during the write operation toprogram the first memory cell. The logic may also cause a third biasvoltage to be applied to the second word-line during the write operationto provide the third bias voltage to the second memory cell to reducevoltage bias to the second memory cell due to the second bias voltageapplied to the bit-line to program the first memory cell, the third biasvoltage less that the second bias voltage.

Example 18

The system of example 17, the first and third bias voltages may beseparate positive voltage biases.

Example 19

The system of example 17, the third bias voltage may reduce voltage biasto the second memory cell by at least 1 volt during the write operation.

Example 20

The system of example 17, the write operation may be a RESET operationto program the first memory cell.

Example 21

The system of example 17 may also include one or more additional memorycells coupled with the bit-line. The system may also include a bit-linedriver coupled with the bit-line. For these examples, the first memorycell may be physically located on the bit-line in a position farthestaway from the bit-line driver as compared to the second memory cell andthe one or more additional memory cells.

Example 23

The system of example 17, the first and second memory cells may includenon-volatile memory.

Example 24

The system of example 22, the non-volatile memory may include phasechange memory that uses chalcogenide phase change material, flashmemory, ferroelectric memory, SONOS memory, polymer memory, FeTRAM,FeRAM, ovonic memory, nanowire, EEPROM, PCM, memristors or STT-MRAM.

Example 25

The system of example 17 may also include one or more of one or moreprocessors communicatively coupled to the controller, a networkinterface communicatively coupled to the system, a battery coupled tothe system or a display communicatively coupled to the system.

It is emphasized that the Abstract of the Disclosure is provided tocomply with 37 C.F.R. Section 1.72(b), requiring an abstract that willallow the reader to quickly ascertain the nature of the technicaldisclosure. It is submitted with the understanding that it will not beused to interpret or limit the scope or meaning of the claims. Inaddition, in the foregoing Detailed Description, it can be seen thatvarious features are grouped together in a single example for thepurpose of streamlining the disclosure. This method of disclosure is notto be interpreted as reflecting an intention that the claimed examplesrequire more features than are expressly recited in each claim. Rather,as the following claims reflect, inventive subject matter lies in lessthan all features of a single disclosed example. Thus the followingclaims are hereby incorporated into the Detailed Description, with eachclaim standing on its own as a separate example. In the appended claims,the terms “including” and “in which” are used as the plain-Englishequivalents of the respective terms “comprising” and “wherein,”respectively. Moreover, the terms “first,” “second,” “third,” and soforth, are used merely as labels, and are not intended to imposenumerical requirements on their objects.

Although the subject matter has been described in language specific tostructural features and/or methodological acts, it is to be understoodthat the subject matter defined in the appended claims is notnecessarily limited to the specific features or acts described above.Rather, the specific features and acts described above are disclosed asexample forms of implementing the claims.

The invention claimed is:
 1. An apparatus comprising: a controller for amemory device, the controller to include logic, at least a portion ofwhich is implemented as hardware, the logic to: cause a first biasvoltage to be applied to a first word-line coupled with a first memorycell included in the memory device and cause a second bias voltage to beapplied to a bit-line coupled with the first memory cell and a secondmemory cell included in the memory device, the first bias voltage andthe second bias voltage to be applied during a write operation toprogram the first memory cell; and cause a third bias voltage to beapplied to a second word-line coupled with the second memory cell duringthe write operation to program the first memory cell, the third biasvoltage applied to the second word-line to cause a reduction in voltagebias to the second memory cell due to the second bias voltage applied tothe bit-line to program the first memory cell, the third bias voltageless that the second bias voltage.
 2. The apparatus of claim 1,comprising the first and third bias voltages are separate positivevoltage biases.
 3. The apparatus of claim 1, comprising the third biasvoltage to reduce voltage bias to the second memory cell by at least 1volt during the write operation.
 4. The apparatus of claim 1, the writeoperation comprising a RESET operation to program the first memory cell.5. The apparatus of claim 1, wherein one or more additional memory cellsare included in the memory device, the one or more additional memorycells coupled with the bit-line, the memory device also includes abit-line driver coupled with the bit-line and the first memory cellincluded in the memory device is physically located on the bit-line in aposition farthest away from the bit-line driver as compared to thesecond memory cell and the one or more additional memory cells.
 6. Theapparatus of claim 1, the first and second memory cells of the memorydevice include non-volatile memory.
 7. The apparatus of claim 6, thenon-volatile memory comprising phase change memory that useschalcogenide phase change material, flash memory, ferroelectric memory,silicon-oxide-nitride-oxide-silicon (SONOS) memory, polymer memory,ferroelectric polymer memory, ferroelectric transistor random accessmemory (FeTRAM or FeRAM), ovonic memory, nanowire, electrically erasableprogrammable read-only memory (EEPROM), phase change memory, memristorsor spin transfer torque magnetoresistive random access memory(STT-MRAM).
 8. The apparatus of claim 1, comprising one or more of: oneor more processors communicatively coupled to the controller; a networkinterface communicatively coupled to the apparatus; a battery coupled tothe apparatus; or a display communicatively coupled to the apparatus. 9.A method comprising: causing, by a controller for a memory device, afirst bias voltage to be applied to a first word-line coupled with afirst memory cell included in the memory device; causing a second biasvoltage to be applied to a bit-line coupled with the first memory celland a second memory cell included in the memory device, the first biasvoltage and the second bias voltage to be applied during a writeoperation to program the first memory cell; causing a third bias voltageto be applied to a second word-line coupled with the second memory cellduring the write operation to program the first memory cell, the thirdbias voltage applied to the second word-line to cause a reduction involtage bias to the second memory cell due to the second bias voltageapplied to the bit-line to program the first memory cell, the third biasvoltage less that the second bias voltage.
 10. The method of claim 9,comprising the first and third bias voltages are separate positivevoltage biases.
 11. The method of claim 9, comprising the third biasvoltage to reduce voltage bias to the second memory cell by at least 1volt during the write operation.
 12. The method of claim 9, the writeoperation comprising a RESET operation to program the first memory cell.13. The method of claim 9, comprising the first memory cell physicallylocated on the bit-line in a position farthest away from a bit-linedriver for the bit-line as compared to the second memory cell and one ormore additional memory cells also coupled with the bit-line.
 14. Themethod of claim 9, the first and second memory cells includingnon-volatile memory.
 15. The method of claim 14, the non-volatile memorycomprising phase change memory that uses chalcogenide phase changematerial, flash memory, ferroelectric memory,silicon-oxide-nitride-oxide-silicon (SONOS) memory, polymer memory,ferroelectric polymer memory, ferroelectric transistor random accessmemory (FeTRAM or FeRAM), ovonic memory, nanowire, electrically erasableprogrammable read-only memory (EEPROM), phase change memory, memristorsor spin transfer torque magnetoresistive random access memory(STT-MRAM).